Hydraulic fracturing is a process commonly used to increase the flow of fluids, such as oil and gas, from a portion of a subterranean formation. Hydraulic fracturing operations generally involve placing a fracturing fluid into a formation or zone at a rate and pressure sufficient to cause the formation to break and form one or more fractures. The fracturing fluids provide two functions, the first is to provide the pressure needed to fracture the formation and the second is to transport solid particles into the fracture to keep the fracture open once the pressure is released and the overburden is permitted to settle. The solid particles, known as proppant or propping agents, can be of various types, such as graded sand, bauxite, ceramics, etc., which are suspended in the fracturing fluid and then deposited in the fractures. By keeping the fracture from fully closing, the proppant particulates aid in forming conductive paths through which fluids may flow. The degree of success of a fracturing operation depends, at least in part, upon fracture conductivity once the fracturing operation has ceased and production has commenced. The fracture conductivity depends, at least in part, on the consistency of the proppant within the fractured formation, which can be deteriorated if a significant amount of the proppant flows back out of the formation. Controlling the proppant flow-back during and after fracturing operations can be critical to the treatments success.
Acid fracturing is a process commonly used to increase the flow of fluids, such as oil and gas, from a portion of a subterranean formation. Acidizing operations are generally proppant free and involve acid etching on a fracture surface. This creates increased fracture conductivity only if the etching can help prevent fracture closure. Acid reacting with carbonate reservoirs can produce a wormholing effect of conductive channels, but the channels can collapse due to high closure stress and have very low retained conductivity.
To extend and sustain acid fracture conductivity the use of both proppant fracturing and acid fracturing methods can be combined. The use of retarded acids has shown advantages when the combined method of acid fracturing with proppant is used. In high stress formations and high production wells, proppant crushing and proppant flowback can present serious problems.
Thus, a need exists for a practical method of performing acid fracturing with proppant with a system that inhibits proppant crushing and flowback.